Bob, 45 pounds of KE = just that, 45 pounds of KE at 5 yards and at 45 yards. It doesn't matter.
As to acceleration vs deceleration, Once the arrow nock leaves the string the arrow starts decelerating. There is no more acceleration. It can't happen! If you believe so, please explain how this occurs.
If the arrow had 45 pounds KE when it left the bow and your question dealt with 5 yards and 45 yards with this same arrow, I don't think there is an issue as it won't be 45# KE at either location.
My 2 cents
Greg
"Getting close to the game is the joy of Bowhunting for me, the harvest is a bonus."
Live 15 ft Python after eating a small Antelope!